Color photographic film having extended exposure-response characteristics

ABSTRACT

A color photographic film with extended exposure response characteristics having a plurality of emulsion layers divided into sets, each set having a different photographic speed. The emulsion layers within a set have the same photographic speed but each layer is responsive to a different region of the spectrum. The emulsion layers are arranged either one above the other or side-by-side in a geometric pattern and all have D-log characteristic curves which have substantially equal slopes. The effective speed of one set is adjusted such that it commences responding to impinging light as another set approaches saturation. This is accomplished either by selection of the basic sensitivities of the various emulsions or by the use of auxiliary means such as attenuating filters. Dye-forming couplers may be incorporated during manufacture in all emulsion layers or may be introduced during processing. The invention may also be incorporated into a number of embodiments employing either the diazo or diffusion transfer processes. In addition apparatus employing the principles of the invention is described.

United States Patent Wyckoff [54] COLOR PHOTOGRAPHIC FILM HAVINGEXTENDED EXPOSURE- RESPONSE CHARACTERISTICS [72] Inventor: Charles W.Wyckoff, Needham, Mass.

[73] Assignee: Applied Photo Sciences, Inc., Newbury,

Mass.

[22] Filed: Nov. 14, 1969 [21] Appl. No: 876,626

Related US. Application Data [63] Continuation-impart of Ser. No.445,496, Apr. 5, 1965, abandoned, which is a continuation-in-part ofSer. No. 98,176, Mar. 24, 1961, Pat. No. 3,450,536.

[15] 3,663,228 [451 May 16, 1972 Primary ExaminerDavid Klein AssistantE.\'aminer-Mary F. Kelley Attorney-Ralph L. Cadwallader [57] ABSTRACT Acolor photographic film with extended exposure response characteristicshaving a plurality of emulsion layers divided into sets, each set havinga different photographic speed. The emulsion layers within a set havethe same photographic speed but each layer is responsive to a differentregion of the spectrum. The emulsion layers are arranged either oneabove the other or side-by-side in a geometric pattern and all haveD-log characteristic curves which have substantially equal slopes. Theeffective speed of one set is adjusted such that it commences respondingto impinging light as another set approaches saturation. This isaccomplished either by selection of the basic sensitivities of thevarious emulsions or by the use of auxiliary means such as attenuatingfilters. Dye-forming couplers may be incorporated during manufacture inall emulsion layers or may be introduced during processing. Theinvention may also be incorporated into a number of embodimentsemploying either the diazo or diffusion transfer processes. In additionapparatus employing the principles of the invention is described.

11 Claims, 17 Drawing Figures PATENTEBHAYIS I972 3. 663,228

SHFU 3 0F 4 FIG. 3.

IN VEN TOR.

CHARLES W. WYCKOFF BY EATENTEDMAY 16 1972 SHEET 4 BF 4 2.0 LOG RELATIVEEXPOSURE FIG. 4A.

LOG RELATIVE EXPOSURE FIG. 4B.

1 N VENTOR CHARLES W. WYCKOFF BY (41/ K COLOR PHOTOGRAPHIC FILM HAVINGEXTENDED EXPOSURE-RESPONSE CHARACTERISTICS This application is acontinuation-in-part of my copending application Ser. No. 445,496, filedApr. 5, 1965, now abandoned. Application Ser. No. 445,496 was acontinuation-inpart ofapplication Ser. No. 98,176, filed Mar. 24, 1961,which issued as U. S. Letters Pat. No. 3,450,536 on June 17, 1969 forSilver Halide Photographic Film Having Increased Exposure-ResponseCharacteristics."

This invention relates to photosensitive materials and more particularlyto color sensitive photographic films and the like having improvedexposure-response characteristics.

The common invention described in said copending application Ser. No.445,496 and the present application was made in the performance of workunder a NASA contract and is subject to the provisions of Section 305 ofthe National Aeronautics and Space Act of 1958, Public Law 85-568 (72State. 435; 42 U.S.C. 2457).

Heretofore, photographic color films have exhibited a usefulexposure-response range which was somewhat less than three decades. Thisresponse is limited by the physical characteristics of the variousemulsions employed in color films. The aforementioned patent teaches asuccessful photographic film having a tremendous exposure-responserange. This is basically a black and white film but color is used in theemulsions to distinguish the images recorded in the various layers. Thatfilm has proven to be of great value in the scientific community as wellas in other fields where wide exposure latitude was a requirement. Itwas immediately evident that a color film having an extendedexposure-response range would be a valuable and useful tool. The presentinvention adds the benefit of recording the object with greater colorfidelity than the structure of the aforementioned patent permitted.

It is, therefore, an object of this invention to provide a photographicmaterial capable of recording, in color, objects and phenomena havinggreat exposure ranges.

Another object of this invention is to provide a new and very fastphotographic emulsion for use in. color photography.

A further object of this invention is to provide a simple colorphotographic film which may be used in simple cameras as well as themost complicated remote control photographing apparatus.

Other and further objects of this invention will be pointed out in thefollowing specifications and appended claims. In summary,'this inventionis an extended exposure range color photographic film having a pluralityof emulsions divided into pairs or groups" and sets. As used herein theemulsions in a pair or group have different speeds but similar spectralsensitivities, while the emulsions in a set have different spectralsensitivities but similar speeds.

The invention will be more clearly understood by referring to thefollowing description in conjunction with the attached drawings,wherein:

FIGS. 1A, 1B, 1C,1D, 1E, 1F,1G, 1H and ll are enlarged, cross-sectionalviews of various embodiments of this invention;

FIGS. 2A, 2B, 2C, 2D and 2E are schematic views of this inventionincluded for explanatory purposes to indicate various degrees ofexposure of certain photographic emulsions;

FIG. 3 is a schematic view of a modification of the invention in whichthe object is separately recorded on two portions of the same film; and

FIGS. 4A and 4B are Density-log Exposure graphs showing typicalsensitivity curves for various emulsions used in negative and reversalfilms respectively.

Throughout the following description of this invention, variousemulsions will be referred to as being sensitive to certain colors suchas red-sensitive," green-sensitive and bluesensitive. In this regard,these terms are employed in the broad technical sense to mean differentportions of the visible spectrum, such as the red region from about 600to 700 nm, the blue region from about 400 to 500 nm and the green regionfrom about 500 to 600 nm. It is not the applicant's intention to setprecise limitations but rather to make useful approximations that willbe helpful in understanding this invention. It is important for certainapplications that the spectral sensitivity extend into the infrared andultraviolet regions. Thus, the references to red-sensitive,green-sensitive and blue sensitive emulsions must not be interpreted tocover these specific wavelengths alone but must be recognized to bebroad divisions of the light spectrum, which may include infrared andultraviolet, or substantial portions thereof. There may also be someoverlapping between emulsions sensitive to adjacent regions. Realizingthe broader meaning of these terms, the preferred embodiment is adivision of the visible spectrum into three substantially equal parts ofabout nm each starting at 400 nm with blue, followed by green and red,the blue region being sensitive to at least some ultraviolet and the redresponding to at least some infrared.

Referring first to FIG. 1A, there is shown a photographic productconsisting of a film base 10, a pair of red'sensitive photographicemulsions 20 and 21, coated in layers upon base 10. A second pair ofphotographic emulsions 30 and 31, sensitive to light within the greenregion of the spectrum, are coated in layers above emulsion 20. Theuppermost layers of this film consist of emulsions 40 and 41 which areblue-sensi tive emulsions. The photographic emulsions which constitutethe various layers of this film may be selected from any of thewell-known photosensitive emulsions that perform the necessary functionsof this invention. Preferably emulsions 20, 30 and 40 have substantiallythe same photographic speed. This means that they respond to the samelevels of exposure for light within the region of the spectrum to whichthey are sensitive. For this reason, curve A in FIG. 4A represents theD-log E curve, for each of emulsions 20, 30 and 40. Curve A indicatesthat these emulsions begin to respond to light at a very low exposurelevel of about 0.4 on the log Relative Exposure scale. As the exposureincreases, the color density in the emulsion increases until it reachesa saturation point at an exposure level of about 3.0 where the colordensity remains constant re gardless of increases in exposure. Note thatthese emulsions demonstrate a total exposure response of about threedecades and a linear range of about two decades. This response range maybe increased or decreased by varying the thickness of the emulsions orby the addition of sensitizers or desensitizers but the range indicatedis a practical and useful one.

Emulsions 21, 31 and 41 in FIG. 1A have substantially the samephotographic speeds and are represented by curve B in FIG. 4A. Theseemulsions begin to respond to light within their respective regions ofthe spectrum at about 2.5 and the color density increases as exposureincreases to a saturation point at approximately 5.5. Curve C is thetotal or accumulated density of the combination of curves A and B. Notethat it has a total exposure response of about five decades and a linearresponse of at least four decades. The feature of curve A leveling offin the region where curve B begins to respond produces a straight lineresult in curve C which we shall refer to throughout this application ascomplementary speeds". Note that curves A and B have substantially equalslopes. Without this novel feature curve C would not have the straightline result illustrated.

Each of these emulsions are preferably color sensitized photographicsilver halide emulsion layers. Emulsions 20, 30 and 40 are the fasteremulsions and it is desirable to use a very fast emulsion such as onehaving an exposure index of 1000. Emulsions 21,31 and 41 havecomplementary speeds to em ulsions 20, 30 and 40, respectively and thusexposure indexes of 10 are preferred. The silver halide in each emulsionis sensitized to respond to certain regions of the spectrum. Colorsensitizers for this purpose are well known. Emulsions 20 and 21 aresensitive to red light and may employ any of a number of red sensitizerssuch as:

l, 1 diethyl 4, 4' carbocyanine iodide (kryptocyanine) 3, 3'diethylthiadicarbocyanine iodide l, l diethyl 4, 5, 4, 5'dibenzothiacarbocyanine bromide l, I diethyl 2, 2 cyanine iodide, 2 (pdiethylaminostyryl) benzothiazole Color sensitizers for thegreen-sensitive emulsions 30 and 31 may be any of those well known inthe art such as, for example:

1, 1 diethyl 6, 6 diethoxy 2, 4 cyanine bromide (pinachrome) 1, 1'diethyl 6, 6 dimethyl 2, 4 cyanine bromide (orthechrome T) 1, 1' diethyl2, 2 carbocyanine iodide (pinacyanol) 3, 3' diethylthiacarbocyanineiodide 3, 3' diethylselenacarbocyanine iodide 3, 3 diethyl 9methylthiacarbocyanine bromide No special color sensitizers need be usedfor the blue-sensitive emulsions 40 and 41 since most emulsions arenaturally bluesensitive.

In some cases, it is preferable to employ reversal-type emulsions inwhich the dye-forming couplers are introduced during processing becausethey can be made photographically faster than emulsions which containthe dye-forming couplers. Curves A and B in FIG. 4B show reversalemulsions having substantially the same characteristics as the emulsionsshown in FIG. 4A except that at minimum exposure, maximum color densityis present. As exposure increases, density decreases until it reaches aminimum density. Curve C is the accumulated densities of curves A and B.The same color sensitizers may be used in reversal film and the samerequirement for complementary speeds is present.

FIG. 1B shows an extended-exposure range color-photographic film whichemploys means to adjust the spectral response of some of the emulsions.This is accomplished by inserting certain color filters between theemulsion layers, specifically between pairs of emulsions, or byincorporating within the emulsions colored dyes of the propersaturation. FIG. 1B shows the three pairs of emulsions shown in FIG. 1Awith the addition of color filters l2 and 14. Emulsions 40 and 41 areblue sensitive and record incident radiation in that region of thespectrum. Color filter 12 is disposed between the blue-sensitiveemulsions 40 and 41, and the green-sensitive emulsions 30 and 31. Filter12 is yellow and blocks the passage of blue light which was useful inexposing emulsions 40 and 41 but which could introduce error intoemulsions 30 and 31. Magenta filter 14, between the green-sensitiveemulsions 30 and 31 and the red-sensitive emulsions and 21, prevents thepassage of green light into the red-recording region. In FIG. 1B, thecolor filters 12 and 14 are introduced to help correct thecharacteristics of the emulsions to insure greater accuracy in therecording of objects. This is particularly useful when the colorsensitivity of the lower emulsions overlap those of the higheremulsions. For example, if the spectral sensitivity of emulsion extendsthrough the green and blue regions, then it is essential to filter outthe blue light before it reaches emulsion 30 which has a prime functionof recording green light. Yellow filter 12 serves this purpose. Thecombination of yellow filter 12 and magenta filter l4 insures that onlyred light reaches emulsions 20 and 21. Some sets of emulsions may needonly a single color filter while other sets may require both filters.

As the aforementioned patent points out, there are times when it isdifficult to obtain photographic emulsions having perfectlycomplementary speeds. The solution to this problem is disclosed in thepatent. A neutral density filter is interposed between the emulsionlayers to shift the D-log E curve of the lower emulsion so that itseffective speed is complementary to that of the upper emulsion. In FIG.1C there are disclosed two photographic color films or sets with aneutral density filter l6 interposed between them. Neutral densityfilter 16 may be, for example, colloidal silver dispersed in a gelatinsubstrate. Other neutral density filters are well-known in this art andmay be used. The value of filter 16 is selected to shift the D-log Ecurve of the slower blue emulsion 41 so that it is complementary to thefaster blue emulsion 40. Similarly, the red and green sensitiveemulsions 21 and 31 respectively, are also shifted to becomecomplementary with emulsions 20 and 30.

By the use of this filter, greater flexibility is provided in selectingcolor films that have the more favorable spectral response withoutconcern for the relative speeds of the films. Any discrepancy in thespeeds of the two emulsions is remedied by the use of the proper neutraldensity filter 16 to make their effective speeds complementary.

FIGS. 1A, 1B and 1E are shown having three pairs of emulsions, each pairbeing sensitive to a different region of the spectrum. As may be seenfrom FIG. 4A and curves A and B therein, the use of pairs of emulsionsprovides total exposure range of nearly six decades or at least 100,000to 1. If, however, even greater exposure latitude is desired, then athird emulsion having complementary speed to one of the other emulsionsmay be added as shown in FIG. 1D. In this figure, a third emulsion oflow speed has been added for each of the colors. Emulsion 22 isred-sensitive, emulsion 32 green-sensitive and emulsion 42 isblue-sensitive. In fact, the only serious limitation to the number ofphotographic emulsions that may be used is the scattering effectproduced by the total thickness of all the emulsion layers and thedispersion of light passing therethrough. It should be pointed out thatvarious combinations may be made utilizing the principles describedherein.

FIG. 1E shows a photographic product having three pairs of emulsions anda number of color filters interposed between the layers to control theexposure of the emulsions. The top layer is a blue-sensitive emulsion 40which responds to incident blue light as shown by curve A in FIG. 4A.Blue-sensitive emulsion 41 is disposed beneath emulsion 40 but may havethe same speed as emulsion 40. To shift the D-log E curve or theeffective speed of emulsion 41 so that it has a complementary speed toemulsion 40 without affecting either the photographic speed or thespectral sensitivity of any lower layers, a yellow filter 11 is insertedbetween emulsions 40 and 41. Filter 11 will attenuate blue light only,thus permitting the green and red images to freely pass therethrough. Itmust have a predetermined color density to attenuate the correctproportion of the incident blue light to effectively shift the speed ofemulsion 41 until it is complementary to that of emulsion 40. Theattenuation of filter 11 must be selected in accordance with the speedsof emulsions 40 and 41. As an example, it may pass 10 percent of theblue light incident thereupon and attenuate percent, thus producing theeffect of a density 1.0 filter. If it passed only 1 percent of theincident blue light then it has the effect of a density 2.0 filter. Thedegree of attenuation is dictated by the speeds of the emulsions and howfar the D-log E curve of the slower emulsion must be shifted.

A second yellow filter 12 is disposed intermediate emulsions 41 and 30.This yellow filter 12 completely blocks the passage of any blue lightbut permits red and green light to pass therethrough. Intermediate thetwo green sensitive layers 30 and 31 is a magenta filter 13, designed toblock a predetermined portion of the green light and freely pass redlight. The attenuation provided by filter 13 must be sufficient to shiftthe effective speed of emulsion 31 to render it complementary toemulsion 30. A magenta filter 14 is disposed between emulsions 31 and 20to block all green light at this point. The effect of yellow filter 12and magenta filter 14 is to allow only red light to expose emulsions 20and 21. Intermediate emulsions 20 and 21 is a further filter 15 toattenuate this red light, thus shifting the effective speed of emulsion21 until it is complementary to emulsion 20. This filter 15 may beeither cyan or neutral. A cyan filter blocks red light. It may beneutral because the only light passing therethrough is red, due to theeffect of the yellow and magenta filters 12 and 14 above. In using theconstruction shown in FIG. 1E, the benefits mentioned with regard toFIGS. 1B and 1C are combined. The speeds of emulsions 21, 31 and 41 neednot be complementary to emulsions 20, 30 and 40 originally. The filterswill shift their effective speed to make them complementary. Thespectral sensitivity of emulsions 20, 21, 30 and 31 need not be limitedto their precise spectral region. Corrections in both speed and spectralsensitivity are provided by the filter elements. In the film of FIG. 1E,the speeds of emulsions 21, 31 and 41 need not be similar because theyare individually shifted by different filters which do not affect otheremulsions. In fact, the speeds of emulsions 20, 30 and 40 may also beadjusted by color filters if necessary, but such filters would alsoaffect the slower emulsions, which would be shifted by the total effectof such a filter and the filter of the same color mentioned above.

This invention may also be utilized in other physical structures thanthose described above. One such embodiment is a number of thin emulsionlayers for each color, coated on the film support. The size of thesilver grains are predetermined to be substantially uniform within eachemulsion but to vary from emulsion layer to emulsion layer to producedifferent and complementary speeds. Although it is not essential, it ispreferable to coat the emulsion with the smallest silver grains closestto the film support. Additional layers are coated in sequence above thisfirst layer and the silver grains in each layer are progressivelylarger. The total amount of silver in each emulsion should besubstantially equal to the silver content in each of the otheremulsions. As is well known, the sensitivity of an emulsion with largesilver grains is considerably faster than those with small silvergrains. The silver content of each emulsion is intentionally made sparsein order to reduce light dispersion and associated scattering.Preferably the thin emulsions are k to 2 microns thick, more or less,and the number of emulsion layers is determined by the total responserange and the purity of spectral sensitivity desired. To equate thistype of film with those defined above, a total response range of fivedecades on the log E axis is recommended and five thin layers accomplishthis goal.

As an example, the top layer may contain large silver halide grains withthiourea sensitization for maximum speed. Such a layer, upon exposureand development, would yield a D-log E curve of low slope and density.It would have an exposure range of or more to l. The next lower thinemulsion will contain smaller crystals about one quarter the size of thetop layer and these will also be sulphur sensitized to produce aboutone-tenth the sensitivity of the top emulsion layer. The actual speedmay be adjusted to make the exposure start where the top emulsionceases, thus producing the effect of an extended D-log E curve. Theslope of all layers is kept substantially identical by maintaining thesame silver concentration and grain size ratio in each layer.

Another embodiment of this invention is a single blended emulsion layerfor each color. The blend would have a low silver content and havesubstantially uniform quantities of each grain size of silver halide toproduce a response range in the region, for example, offive decades.

The low silver content in the above-mentioned photographic productswould develop to a low contrast silver image. Thus, it is important thatduring the color development stage, a greater concentration of dye beemployed in order to compensate for this low contrast. The color D-log Ecurve for each of these emulsions may be shown by curves C and C inFIGS. 4A and 4B respectively. Each emulsion layer has incorporatedtherein a color sensitizer as previously described.

The neutral density filter 16, in FIG. 1C and the color filters 11,12,13 and 14 in FIGS. 1B, 1D and 1E and filter 15 in FIG. 1E, which may beeither neutral or cyan, are preferably of a soluble or bleachablematerial that may be dissolved and washed away or otherwise disposed ofduring processing. This is important because these filter materialscould interfer with the viewing and printing of the image recordedtherein. In FIG. 1C, for example, filter 16 would upset thecomplementary speeds of the emulsions produced by the filter itselfduring exposure. In FIG. 1B and 1D color filters 12 and 14 (and in FIG.1E, color filters 11 and 13) would prevent the images recorded in eachemulsion from being properly viewed or printed, thus greatly reducingthe films usefulness. By using soluble or bleachable color filters,these materials are removed or rendered colorless during the processingstage. Bleachable color filters are preferred over their solublecounterparts because they may be made colorless quite simply indeveloping and processing. In the case of neutral density filters,however, the soluble type has proven satisfactory and may have equalstatus with bleachable neutral density filters. These elements areremoved or rendered colorless during processing so that they performtheir function during exposure but do not lessen the usefulness of theproduct during viewing and printing.

There are many well-known forms of color filters that may be used forthe color filters 11, 12, 13, 14 and 15 in FIGS. 18, 1D, and 1E. Theyellow filters 11 and 12 may be, for example, a bleachable yellowcolloidal silver. Dyes may also be used in the filter layers ofaphotographic film. One example of a yellow filter made from a dye isAniline Yellow, C. I. No. 1 1,000 (Absorption Peak about 457mm). Amagenta filter may be made from Acid Red 12, C. I. No. 14,835(Absorption Peak about 550mm). During the processing of the film, thesedyes, which are colored as shown, could be made colorless by treatingthem in a reducing agent solution such as sodium hydrosulfite. Thiswould reduce the dye to a permanently colorless substance.

FIGS. 2A, 2B and 2C show only one of the three pairs of emulsions ofFIGS. 1A, 1B, 1C or IE to simplify the explanation of the applicantsinvention. The red-sensitive emulsions 20 and 21 have been selected fordiscussion, but the explanation applies to the other pairs of emulsionsas well. FIG. 2A illustrates sufficient light passing from object 17through lens 18 to expose only the more sensitive emulsion 20. Theobject 17 is shown consisting of five areas identified by the referencedesignators 24 to 28 inclusive, where area 24 emits an intense level ofred light and area 28, a low level, and areas 25 and 26 and 27 are ofintermediate intensities, area 27 being the weakest area and area 25 thebrightest of the three. Lens 18 reverses the relative positions of theareas 24 to 28 when the emulsion is exposed to light coming therefrom.The image of area 28 falls in film portion 81. Since little lightarrives from darkest area 28, this film portion 81 is only slightlyexposed and therefore is shown clear. The light from clear area 24totally exposes film portion which is shown black in the figure toindicate total exposure of the emulsion. The intermediate areas 25, 26and 27 of object 17 produce exposures of different degrees as shown byfilm portions 84, 83 and 82 respectively. It should be pointed out thatthe areas of object 17 are shown with different degrees of blackening toindicate different levels of intensity while emulsion 20 is shown withdifferent degrees of blackening to depict different degrees of exposure.

In FIG. 2A, the light from the object 17 is sufficient to expose onlythe more-sensitive emulsion 20 but not sufficient to expose theless-sensitive emulsion 21. In other words, the range of light energystriking emulsions 20 and 21 would all be found along curve A of FIG. 4Ato the left of the point where curve B begins to respond. Here, therange oflight levels striking the emulsion is perfectly matched to theexposureresponse of emulsion 20. Therefore, emulsion 21 does not respondat all, due to the fact that it is insensitive to the level oflightenergy passing through emulsion 20.

Now consider the case where the light energy striking the film isincreased many times. This may be done by greatly increasing the lightenergy incident upon object 17 or by greatly extending the time duringwhich the emulsions are exposed to light. FIG. 2B shows the effectofsuch an exposure upon emulsions 20 and 21. The more-sensitive emulsion20 is totally saturated as indicated by the blackening of film portions81 to 85 inclusive. The light energy which passes through emulsion 20and is available to expose emulsion 21 causes the same degree ofexposure of film portions 86 to 90 of emulsion 21 as was produced infilm portions 81 to 85 respectively of emulsion 20 of FIG. 2A. FIG. 2Bindicates that the range of light energy incident upon the emulsionswould all fall along curve B in FIG. 4A to the right of the point wherecurve A levels off. In this case, we can see that the range of lightintensity striking the emulsions is perfectly matched to theexposure-response range of emulsion 21.

A third case to be considered is the instance where the range of lightintensity striking the emulsions is not perfectly matched to theexposure-response range of either of emulsions 20 or 21 but is in therange including portions of curves A and B of FIG. 4A. FIG. 2C shows theeffect of this third case on emulsions 20 and 21. Light from darkestarea 28 of object 17 partially exposes film area 81 of emulsion 20. Morelight comes from area 27 to partially expose to a greater degree filmportion 82. The light from areas 27 and 28 is insufficient to exposefilm portions 86 and 87 of emulsion 21. The light passing from 26 issufficient to totally expose film portion 83 but is not sufiicient toexpose film portion 88 of emulsion 21. The light from area 25 is notonly sufficient to expose film portion 84 of emulsion 20 but also topartially expose film portion 89 of emulsion 21. The light from thelightest area 24 of object 17 saturates film portion 85 and partiallyexposes film portion 90 to a greater extent than film portion 89.

It can thus be seen that with tremendous differences in the lightintensity, useful and accurate reproductions of object 17 can be madefrom the negatives shown in FIGS. 2A, 2B and 2C, In the case of thenegative in FIG. 2A, a positive image of object 17 can be printed fromthe exposure of emulsion 20, after the negative has been developed. Theimage recorded in emulsion 21 of FIG. 28 may also be printed. Thesaturated red-sensitive emulsion 20 becomes a uniformly deep cyan, andto print the cyan image recorded in emulsion 21, the additive effect ofthe two emulsions must be considered and thus the light used in printingmust be either very intense or its time duration extended. Withreference to the negative of FIG. 2C, a print of the two combinedemulsions can be made by adjusting the printing exposure to reproduceobject 17 from portions of emulsions 20 and 21.

FIG. 2D shows, schematically, the exposure of a set having threeemulsions such as red-sensitive emulsions 20, 21 and 22 in FIG. 1D to anobject 17' where there is a tremendous difference between the light fromthe lightest area 24 and the light from the darkest area 28. This lightrange is in excess of the exposure-response range of each of emulsions20, 21 and 22, considered individually.

Light from the darkest area 28 of object 17 almost completely exposesfilm portion 81 of emulsion 20 but does not expose film portions 86 or91 of emulsion 21 and 22. The light from areas 27 and 26' saturates filmportions 82 and 83 and partially exposes to difierent degrees filmportions 87 and 88 but does not expose film portion 92 or 93. The lightfrom area 25 and the lightest area 24 saturates film portions 84, 85, 89and 90 and partially exposes to different degrees, portions 94 and 95.

The extreme range of exposure of object 17 has been recorded by thethree emulsions in its proper degree of exposure and by adjusting theexposure in the printing process, a good reproduction of any portion ofobject 17' can be made. It has been shown that the three emulsionsrecorded the tremendous difference in light levels from the object 17'.It is not, however, possible to accurately print such an exposurebecause of the limited exposure range of currently available printingmaterial, and not because of any limitation of the multi-emulsion filmitself, Any particular portion of the emulsion falling within the rangeof the printing material may, of course, be printed. By decreasing theeffect of the chemical processing, the density contrast can be reduced,thereby providing a means for printing the entire exposure, but theresulting print would not be an accurate reproduction of the originalobject 17.

Thus far we have been discussing the exposure of the emulsions shown inFIGS. 2A, 2B, 2C and 2D in terms of one color only. FIG. 2E shows theeffect of various exposures upon the different emulsion layers. Theelements of the bar graph indicate the relative intensities of thedifferent colors on the object. The range may be in the order of 100,000to l but for simplicity, it shall be shown in eight incrementsidentified by Roman Numerals I to VIII in FIG. 2E and in FIGS. 4A and 4Bas well. The photographic film is shown as a six-layer film having threepairs of emulsions, each pair being sensitive to a different color.Emulsions 20 and 21 are red-sensitive and have complementary speeds withemulsion 20 being faster than emulsion 21. Green-sensitive emulsions 30and 31 also have complementary speeds with emulsion 30 being the faster.The top two emulsions 40 and 41 are blue sensitive and emulsion 40saturates in the region that emulsion 41 begins to respond to bluelight. A lens 18 is shown which reverses the exposure of the film byfocusing the light from the left end of the object on the right end ofthe film segment. Thus, the light from the left end of the object isshown divided into its three components, namely red light 46, greenlight 51 and blue light 56, and focused upon the right hand column offilm segments consisting of segments 65, 70, 75, 80, 85 and 90. For easyreference, the letters r, g" and b have been placed in the color bars toindicate red, green and blue color, respectively. The light from the redportion of the object, designated 46, passes through blue-sensitive filmemulsions 40 and 41 without having any affect upon film segments 65 and70. Similarly, the light from the red portion of the object passesthrough segments 75 and of emulsions 30 and 31 because these emulsionsare sensitive only to light in the green region of the spectrum. Whenthe red light 46 strikes film segment of emulsion 20 it causes anexposure to be recorded there. This exposure is in proportion to theintensity of the red light from the object and causes the exposure to beslightly less than saturation in the region of, for example, IV of FIG.4A. This red light 46 continues and passes through film segment ofemulsion 21 without producing any response therein. Although emulsion 21is red sensitive, the red light 46 produces no exposure therein, becauseits intensity is less than the emulsions threshold of sensitivity. Thisis evident from a view of FIG. 4A, which shows that region IV is at aposition where emulsion B is not activated.

The green light 51 from the object is very intense and not onlysaturates film segment 75 of emulsion 30, but also exposes segment 80 ofemulsion 31 to its point of saturation. This is shown as region VIII ofFIG. 4A. This saturation of film segments 75 and 80 by the green light51 does not affect film segments 65, 70, 85 and 90 because theseemulsions are not sensitive to green light. The blue light 56 is of anintermediate intensity and as such saturates film segment 65 in emulsion40 and also causes a moderate degree of exposure of film segment 70 ofemulsion 41. The intensities of blue light 56 fall in the region VI onthe graph of FIG. 4A.

The red light 47 causes an exposure on film segment 84 of emulsion 20but is not sufficiently intense to cause the exposure of segment 89.This level of exposure is shown as region III in FIG. 4A. Otherexposures caused by the spectral component of the objects light arerecorded in the various segments of the film and correspond to theregions set forth in FIG. 4A. It is noteworthy to observe that thesaturation of certain film segments, for example, film segment 61 inemulsion 40, does not interfere with the recording of a minimum exposureof the emulsions in a different color-sensitive pair, such as filmsegments 81 and 86 in emulsions 20 and 21, The pairs of emulsions areresponsive to their respective color components and in effect arecompletely insensitive to the other colors.

Thus far, we have been discussing the invention in terms of negativetype color film, all layers of which contain dye-forming couplers. Ithas been pointed out, however, that reversal type color film may also beused and, in fact, may even be preferred. In reversal films, densitysaturation is found at minimum exposure and it decreases as exposureincreases until at the limit of its capability, it has a minimum orsubstantially no opaqueness. This is clearly shown by reference to curveA in FIG. 4B. Note that maximum density is found at minimum exposure onthe left side of the graph. As the exposure increases, the densitydecreases as indicated by the downward slope of curve A. When curve Acommences to level off at maximum exposure, curve B begins to respond,thus providing the above mentioned complementary speed. Similarly, curveC is effectively the sum total of the densities of the emulsionsproducing curves A and B. A third reversal type emulsion may be added tothe two shown in the manner described in relation to FIG. 1C. In such acase, the exposure response is increased by approximately three decadesor to more than a million to 1.

When reversal film is developed, a positive image is formed which may beread directly. This may be desirable in certain applications. The filmstructures, shown in FIGS. 1A to 1E may be used with reversal film asreadily as with negative film. The exposures shown in FIGS. 2A to 2Eaccurately apply to reversal film if one remembers that the darkening ofthe film portions is a measure of exposure and not a measure of filmdensity and after completion of the reversal processing the tones ordarkening will be the reverse of those shown in FIGS. 2A and 2E. FIG.413 has also been marked off to show the exposure regions I to VIII asthey relate to the exposure shown schematically in FIG. 2E.

Utility of the invention is improved by using very fast emulsions.Extremely fast speed has been attained by using a fast emulsion of theammoniacal-type having an exposure index of about 1,000. A sensitizer isadded to render the emulsion sensitive to a particular region of thespectrum, for example, redsensitive. No dye-forming coupler is added tothe emulsion. The cyan dye will be added during developing. Byeliminating the dye-forming coupler from the emulsion, the speed isgreatly increased. Actually, it would be more accurate to say that thespeed is held at its high level and not slowed by the addition of thedye-forming coupler. There is another benefit to such a high-speedemulsion without a dye-forming coupler which is a decrease in thescattering effect by dispersion of light waves. The more chemicalssuspended in the emulsion, the greater the scattering effect,

In using this high-speed emulsion, a film structure such as that shownin FIG. 1C is preferred. In this way, three highspeed emulsions 20, 30and 40 are the three top-most layers. The impinging light passes througha minimum of layers, which of necessity, introduce some attenuation. Itis preferable to place the blue-sensitive emulsion 40 on top withgreensensitive emulsion 30 immediately underneath and red-sensitiveemulsion 20 beneath emulsion 30. This arrangement is preferred becausered light passes through emulsion layers more freely than blue and greenlight. Blue light is most susceptible of attenuation and scattering andtherefore belongs on top.

The three top layers, emulsions 20, 30 and 40, in FIG. 1C could becoated alone upon a film support and would provide a new and highlyuseful color film which is faster than any such film now commerciallyavailable. Such a film would add a new dimension to color photography.Although such a photographic emulsion has been known, it has never beenused as an emulsion in a color film without the incorporation of thespeed-decreasing dye-forming couplers. As mentioned above, this elementmay slow the emulsion speed by as much as 50 percent.

The exposed emulsions such as those shown schematically in FIGS. 2A to2E, may be developed in any of the well-known methods for developingnegative and reversal type color films, such as those disclosed in C. E.K. Mees, The Theory of the Photographic Process, Revised Edition, 1954,The MacMil- Ian Company, New York, N. Y., page 584 et seq. (especially587 and 588). As mentioned above, such a tremendous range of exposurecannot be printed on current photographic printing papers because of theinherent limitations thereof. A reason for using reversal type film,since the emulsions develop as positives, is for direct viewing orprojection. In order to reproduce the object, as shown in FIG. 2E, theintensity of the light passing through the developed film must be variedto distinguish details in the highlights which may be found in a highlyexposed portion of the film, such as film segment 80 in emulsion 31. Itwill be noted that the exposure in this segment corresponds to the veryintense green portion 51 of the object. To note the highlights in a lowintensity area or the shadows, such as film segment 81 of emulsion 20,considerably more light is required. By varying the intensity of theexposing light, all the features recorded in the six emulsions of thisphotographic film can be observed and studied. It is also possible tocompensate by varying the spectral composition of the exposing lightifit is desired to increase or to attenuate the particular exposure ofone color with respect to another.

An alternate method of recording objects having extended exposure rangeson color film may be accomplished by the apparatus shown in FIG. 3.Three color-sensitive emulsions 20, 30 and 40 are shown coated on a filmsupport 10. Each of these emulsions has substantially the same speed,but each is responsive to a different portion of the spectrum. Emulsion20 is a red-sensitive emulsion, emulsion 30 is green-sensitive andemulsion 40 is blue-sensitive. A pair of right angle prisms 34 and 35appearing as a cube with a reflecting-transmitting coating applied tothe common surface 36, is disposed in the path of the light from theobject en route to the photographic film. The prisms 34 and 35 act as abeamsplitter. The incident light striking surface 33 of prism 35 passestherethrough and strikes surface 36 and is divided in approximatelyequal proportions; one part passing directly through prism 34 and outthrough surface 37. The other portion is reflected off surface 36 andpasses through prism 35 parallel to the film until it strikes totallyreflecting mirror 38. From mirror 38 the light passes through emulsions40, 30 and 20, in that order, and causes exposures within the emulsionin proportion to the intensity of the light. The light that passesthrough prism 34 also passes through emulsions 40, 30 and 20 but betweenthe prism and the film is a neutral density filter 39. The neutraldensity filter 39 acts substantially in the same manner as filter 16 inFIG. 1C. It shifts the D-log E curve of the portion of the film beneathit a predetermined distance along the exposure axis (see FIGS. 4A and4B). The distance is predetermined so that the exposures producecomplementary speeds in the emulsions. Since the photographic emulsions20,30 and 40 are employed to record the image formed by light passingthrough the neutral density filter 39, and the image formed by lightreflected from mirror 38, the degree of attenuation produced by neutraldensity filter 39 must be proportional to the exposure response range ofthe photographic film, In the case of the photographic emulsion shown inFIGS. 4A and 4B, the emulsion has a linear exposure response range ofapproximately log 2.0. The attenuation produced by filter 39 must beabout log 2.0 which means that 99% of the incident light is attenuatedand 1 percent is passed.

An alternate arrangement for producing the same result, that isside-by-side photographic images on photographic emulsions havingcomplementary speeds, is produced by varying the transmissionreflectioncharacteristic of the reflecting prism surface 36. A partially silveredsurface 36, having an attenuation effect proportional to the exposureresponse of the film completely eliminates any need for the neutraldensity filter 39. This so because the impinging light is divided intotwo parts, the intensity of each being determined bytransmission-reflection characteristics to produce images of differentspeeds.

In using the arrangement of FIG. 3, the film, after development has aseries of exposures which are double images. These double images must bereassembled to accurately reproduce the object. There are many ways inwhich this may be done, but, if the preferred reversal type film isused, the simplest solution is to superimpose the two images inregister, such as by projecting through a similar beamsplitter orcutting the film apart.

In FIG. 3, it is immaterial what reflecting surfaces are employed aslong as the image is not distorted nor serious light losses introduced.Instead of prisms, a particularly useful reflecting surface is a thinreflecting pellicle film which is capable of reflecting and transmittingthe impinging light with a minimum of wasteful internal reflections. Apellicle film may be coated to produce the desired filtering effect.

A photographic film as disclosed herein has great capabilities and maybe used in many applications. It is particularly useful where greatexposure ranges are encountered, such as the detonation of high-powerexplosives, the study of astronomical bodies in the sky and flamestudies of rockets and similar devices. The film, of course, may beproduced in the form of plates, motion picture film or any of thewell-known photographic products.

While the foregoing discussion has been slanted in terms of silverhalide photographic emulsions, arranged in layers, it should now beobvious to those skilled in the art that various other photosensitivematerials may now be used in place of silver halide. For example, thenormally short exposure latitude of diazo materials, when used asduplicating media, may be significantly broadened by utilizing more thanone layer of such material, if the resultant film is constructed inaccordance with the principles of my invention wherein the speed of oneemulsion layer, of the group of blue sensitized layers, is shifted so asto commence responding to impinging light when another emulsion layer(having the same color sensitivity) approaches saturation. However, itshould be understood that the diazo materials are spectrally sensitiveonly to blue-ultraviolet wavelengths.

In the case of the diazo dye, this may be accomplished by means of aneutral density filter layer interposed between the layers or, as analternative to the neutral density filter layer, a yellow colored diazodye can be utilized which will serve to attenuate the impingingblue-ultra violet energy thereby effectively reducing the speed of thelayer beneath it. This filter layer may be incorporated in one or bothof the diazo layers instead of being in a separate layer and should havethe property of becoming colorless either upon exposure to the blueultraviolet energy or when subjected to ammonia or the ammonia fumes used fordevelopment of a normal diazo dye image.

To produce a multi-colored duplicate utilizing diazo materials onestarts with a first monochrome record indicating the spectralreflectance of the scene in a first region of the spectrum. Thereafter,one adds as many other monochrome records of other, different portionsof the spectrum as is necessary to achieve a color facsimile of thescene. Thus, one may have three black and white records, onerepresenting the red content of the scene, another representing thegreen content and, the last, representing the blue content.

The black and white record representing the red content is then used toproduce a cyan colored diazo transparency image. The black and whiterecord representing the green content is then used to produce a magentacolored diazo image while the black and white record representing theblue content is used to produce a yellow colored diazo image. Thereafterthe separate colored diazo image records are registered resulting in acomposite colored facsimile of the original scene.

Assuming the three black and white records are positive reproductions ofthe scene, the following diazo compounds would be used to produce themulticolored facsimile:

Cyan

4-ethy1amino-3-methyl benezene-diazonium borofluoride 1.2 parts Tartaricacid 4 parts H acid 1.9 parts Water 100 parts Magental-diazo-Z-naphthol-4-sulphonic acid 1.0 parts Aluminum sulphate 3.0parts Resorcin 0.6 part Water 100 parts Yellow4-ethyl-amino-3-methyl-benzene-diazoniumborofluoride 1.2 parts Tartaricacid 4.0 parts Phenol 0.5 part Water 100 parts If a two color image isdesired, the cyan image above is combined with one made using thefollowing orange-red sensitizing solution:

1-diazo-2-naphthol-4-sulphonic acid 1.5 partsl-phenol-3-methyl-5-pyrazolone 0.9 part Sulphuric acid 7.2 parts Waterparts If instead the three black and white records are negativereproductions of the scene, the following diazo compounds would be usedto produce the multicolored facsimile:

Cyan

Dianisidine-tetrazo-disulphone 1 part Sodium hydroxide, 3% solution 2.5parts Alcohol 400 parts Glycerin 3 parts l-I Acid 1 part Water 200 partsYellow 2-methyl-benzidine-tetrazo-disulphonate 4 parts Alcohol 200 partsWater 200 parts Glycerin 20 parts Aceto-acetic ester 2 parts MagentaAnisidine-diazo-sulphonate 2 parts Sodium hydroxide, 1% solution 200parts Alcohol 100 parts Glycerin 3 parts Beta-oxy-haphthoic acid 2 partsAfter reviewing the embodiments shown in FIGS. 1A, 13, 1D and IE, itshould become obvious that the principles herein set forth apply to theimage formation process commonly referred to as the diffusion transferprocess," wherein the developing agents and color dyes are incorporatedinto the film as layers separated from the silver halide emulsionlayers. It will be apparent to those skilled in the art that thelight-sensitive emulsions do not contain dye-forming couplers. Theconfigurations that may be brought to mind are shown in the followingFIGS. 1F, 16, III and 11.

Referring now to FIG. 1F, there is shown a photographic productutilizing the layered technique of various speeds in the layers, asapplied to the diffusion transfer process. In this embodiment, the filmis provided with a base member 10, and adjacent thereto, is a layer of alinked developer-colored dye having a cyan color. Coated in layers abovethe developer layer 120 is a first pair of emulsions wherein layer 21 isthe slow speed red-record emulsion while layer 20 represents the fasterspeed record sensitive to light within the red portion of the spectrum.A retardation interlayer 14 is placed atop layer 20 and may serve forone of its purposes the same function as layer 14 in FIG. 1B, 1D and 1E.Layer 14 is placed between the green sensitive emulsions 30, 31 and thered sensitive emulsions 20, 21 principally to provide means forpreventing the premature excursion of linked developer-color dye layerfrom migrating into red-record layers 20 and 21. In addition, it maycontain a magenta dye so as to prevent the passage of green light intothe red-recording region.

Layer 130, containing a linked developer-magenta dye is placed abovelayer 14 and green-record layers 30 and 31 are placed atop developerlayer 130. As in the previous embodiments, layer 30 has a faster speedthan layer 31 so that the speed of one commences to respond to impinginglight when the other emulsion layer approaches saturation.

The green-record layers 30 and 31 are provided with an overlayer 12which may include a yellow filter so that any blue light which may havepassed through the outer emulsions will be filtered before it reachesemulsion 30, whose prime function is that of recording the green lightpresent in the scene. Layer 12 serves the primary purpose of preventingpremature migration of developer of layer into green-record layers 30and 31.

Layer 140, having a linked developer-yellow dye, is placed atop layer12, and the blue-record layers 40 and 41 applied thereto. Theblue-record layer 40 has a faster speed than bluerecord layer 41, inaccordance with the principles hereinbefore set forth.

Referring now to FIG. 16, there is shown a slightly different embodimentthan that presented in FIG. 1F. In the embodiment of FIG. 16, instead ofplacing the two record layers (40 and 41 or 30 and 31 or and 21)adjacent to each other, I separate them by the appropriate linkeddeveloper-colored dye layers 140, 130 and 120, respectively. A layer 12is placed between blue layer 41 and green layer 30 to prevent prematuremigration of any developer other than the layer associated therewithfrom migrating to an undesired layer. In addition it may contain ayellow dye to minimize the passage of any blue light beyond layer 12.Similarly, layer 14 is disposed between green-sensitive layer 31 andred-sensitive layer 20 to prevent premature migration of either layer130 into layer 20 or of layer 120 into layer 31. In addition, layer 14may contain a magenta dye to block the passage of any green light intothe red-recording region.

As in the prior embodiment, my device is provided with a base 10, whichmay not, in all cases, be necessary.

Referring now to FIGS. 1H and 11, there is shown still anotherembodiment of a photographic product utilizing the layered technique asapplied to the diffusion transfer process. In these next two embodimentseach layer is broken up or divided into discrete fast and slow speedportions. For example, in FIG. III, the film is provided with a basemember 10, and adjacent thereto is a linked developer colored dye layer120, having a cyan color. Coated above the developer layer is a pair ofemulsions wherein stripes or dots 21 may represent the slow, red-recordemulsion while stripes or dots 20 represent the faster speed red-record.Retardation layer 14 is placed atop layers 20, 21 and may serve, for oneof its purposes, the same function as layer 14 in FIGS. 18, 1D, 1E, 1Fand 1G. Layer 14 is placed between the green-sensitive emulsions 30, 31and the red-sensitive emulsions 20, 21 principally to provide means forpreventing any premature excursion of linked developer-color dyeparticles of layer 130 from migrating into red-record layers 20 and 21.ln addition, it may contain a magenta dye so as to revent the passage ofgreen light into the red-recording region.

Layer 130, containing a linked developer-magenta dye is placed aboveretardation layer 14 with green-record layers 30 and 31 placed atopdeveloper layer 130. As in the previous embodiments, layers 30 havefaster speeds than layers 31 and may be applied in the form of dots orstripes, the important consideration being that the speed of oneemulsion be adjusted so as to commence responding to impinging lightwhen the other layer approaches saturation.

The green-record layers 30 and 31 are provided with an over layer 12which may include a yellow filter so that any blue light, which may havepassed through the outer emulsions, will be filtered before it reachesemulsions 30 and 31. It being recognized that the prime function ofemulsions 30 and 31 is that of recording the green light present in thescene being photographed. However, the primary purpose of layer 12 isthat of preventing premature migration of developer of layer 140 intogreen-record layers 30 and 31.

Developer layer 140, having a linked developer-yellow dye, is placedatop layer 12, and the blue-record layers 40 and 41 applied thereto inthe form of either dots or stripes. Bluerecord layers 40 have a fasterspeed than blue-record layers 41, in accordance with the principlehereinbefore set forth.

Referring now to FIG. 1], there is shown still another embodiment,utilizing much the same rationale as in FIG. 1H. However, in this latterembodiment, the integrity of the complementary characteristics has beenmaintained by providing a neutral density filter 19.0 which hasalternate light and dark areas 19.1 and 19.2, respectively. In thisembodiment, neutral density filter 19.0 is placed atop or adjacent afilm which has a base 10, a linked developer-cyan dye 120, a red-recordlayer 20, a retardation interlayer 14, a developer-magenta dye layer130, a green-record layer 30 atop layer 130, a retardation interlayer 12atop layer 30, a layer 140 of linked developer-yellow dye atop layer 12and a blue-record layer 40 atop layer 140. Thus, arranged one above theother, discrete complementary speed areas are formed. For those emulsionportions under area 19.2 a slow blue-record portion 40.1, a slowgreenrecord portion 30.1 and a slow red-record portion 20.1 is formed.The remaining blue-record portions 40.0, green record portions 30.0 andred-record portions 20.0, not having been exposed through neutraldensity filter area 19.2, therefore result in a faster speed than itsadjacent portions 40.1, 30.1 and 20.1, respectively.

Although I have disclosed my invention in terms of its preferredembodiment, many variations and modifications will occur to thoseskilled in this art, and all such are deemed to fall within the spiritand scope of this invention.

What is claimed is:

1. A color photographic film comprising a film support;

three pairs of silver halide photosensitive emulsions coated in layersupon the film support, the top pair being responsive to one region ofthe spectrum only, the middle pair being responsive to at least a secondregion of the spectrum and the third pair being responsive to at least athird region thereof;

a first color filter interposed between the two emulsion layers of thefirst pair, said filter blocking a predetermined proportion of lightwithin said one region, the attenuation of said filter beingpredetermined to shift the speed of the lower emulsion of the first pairto provide complementary speeds in the emulsions of the top pair;

a second color filter interposed between the top pair and the middlepair of emulsions, said filter blocking substantially all the lightwithin said one region;

a third color filter interposed between the two emulsion layers of thesecond pair, said filter blocking a predetermined proportion of thelight within said second region, the attenuation of said filter beingpredetermined to shift the speed of the lower emulsion ofthe second pairto provide complementary speeds in the emulsions of the middle pair;

a fourth color filter interposed between the middle pair and the lowerpair of emulsions, said filter blocking substantially all the lightwithin said second region of the spectrum; and

a fifth color filter interposed between the two emulsion layers of thethird pair, said filter blocking a predetermined proportion of the lightincident thereupon, the attenuation of said filter being predeterminedto shift the speed of the lower emulsion to provide complementary speedsin the emulsions of the third pair.

2. A color photographic film as claimed in claim 1 in which the totalspectral response of said pairs of photosensitive emulsions extendsthrough at least the visible spectrum.

3. A color photographic film as claimed in claim 1 in which said fifthfilter is a color filter for blocking said predetermined proportion ofthe incident light in said third region of the spectrum.

4. A photographic film as claimed in claim 1 in which said fifth filteris a neutral density filter for blocking said predetermined proportionof incident light.

5. A color photographic film comprising a film support;

three pairs of silver halide photosensitive emulsions coated in layersupon the film support, the top pair being responsive to blue light only,the middle pair being responsive to at least green light, and the thirdpair being responsive to at least red light;

a first yellow filter interposed between the two emulsion layers of thefirst pair, said filter blocking a predetermined proportion of the bluelight to shift the speed of the lower emulsion of the first pair toprovide complementary speeds in the emulsions of the top pair;

a second yellow filter interposed between the top pair and the middlepair of emulsions to block substantially all the blue light from passingtherethrough;

a first magenta filter interposed between the two emulsion layers of thesecond pair, said filter blocking a predetermined proportion of thegreen light to shift the speed of the lower emulsion of the second pairto provide complementary speeds in the emulsions of the second pair;

a second magenta filter interposed between the middle pair and the thirdpair of emulsions to block substantially all the green light frompassing therethrough; and

a further filter interposed between the two emulsion layers of the thirdpair to block a predetermined proportion of the red light incidentthereupon to shift the photographic speed of the lower emulsion toprovide complementary speeds in the emulsions of the third pair.

6. A color photographic film as claimed in claim in which said furtherfilter is a cyan filter.

7. A color photographic film as claimed in claim 5 in which said furtherfilter is a neutral density filter.

8. A color photographic film comprising:

a film support;

a first set of silver halide photosensitive emulsions coated in layersupon said film support; each emulsion in said first set being responsiveto a different region of the spectrum, the emulsions within said sethaving substantially the same speed;

a second set of silver halide photosensitive emulsions coated in layersabove said first set, the emulsions in the second set havingsubstantially the same spectral response as the emulsions of the firstset; and

a neutral density filter disposed intermediate the two sets, theattenuating effect of said filter being to shift the speed of theemulsions of the lower set a predetermined amount to provide the sets ofemulsions with complementary speeds.

9. A color photographic film as claimed in claim 8 in which said firstand second sets of emulsions have substantially the same photographicspeed.

10. A color photographic film as claimed in claim 8 in which the secondset of emulsions are fast ammoniacal emulsions.

11. A color photographic film comprising:

a film support;

two sets of silver halide photosensitive emulsions coated in layers uponsaid film support, each set containing a red sensitive emulsion, agreen-sensitive emulsion and a bluesensitive emulsion; and

a neutral density filter disposed between the two sets of emulsions, theattenuating effect of the filter being, to shift the speed of the lowerset of emulsions a predetermined amount to provide the two sets ofemulsions with complementary speeds.

nnen

2. A color photographic film as claimed in claim 1 in which the totalspectral response of said pairs of photosensitive emulsions extendsthrough at least the visible spectrum.
 3. A color photographic film asclaimed in claim 1 in which said fifth filter is a color filter forblocking said predetermined proportion of the incident light in saidthird region of the spectrum.
 4. A photographic film as claimed in claim1 in which said fifth filter is a neutral density filter for blockingsaid predetermined proportion of incident light.
 5. A color photographicfilm comprising a film support; three pairs of silver halidephotosensitive emulsions coated in layers upon the film support, the toppair being responsive to blue light only, the middle pair beingresponsive to at least green light, and the third pair being responsiveto at least red light; a first yellow filter interposed between the twoemulsion layers of the first pair, said filter blocking a predeterminedproportion of the blue light to shift the speed of the lower emulsion ofthe first pair to provide complementary speeds in the emulsions of thetop pair; a second yellow filter interposed between the top pair and themiddle pair of emulsions to block substantially all the blue light frompassing therethrough; a first magenta filter interposed between the twoemulsion layers of the second pair, said filter blocking a predeterminedproportion of the green light to shift the speed of the lower emulsionof the second pair to provide complementary speeds in the emulsions ofthe second pair; a second magenta filter interposed between the middlepair and the third pair of emulsions to block substantially all thegreen light from passing therethrough; and a further filter interposedbetween the two emulsion layers of the third pair to block apredetermined proportion of the red light incident thereupon to shiftthe photographic speed of the lower emulsion to provide complementaryspeeds in the emulsions of the third pair.
 6. A color photographic filmas claimed in claim 5 in which said further filter is a cyan filter. 7.A color photographic film as claimed in claim 5 in which said furtherfilter is a neutral density filter.
 8. A color photographic filmcomprising: a film support; a first set of silver halide photosensitiveemulsions coated in layers upon said film support; each emulsion in saidfirst set being responsive to a different region of the spectrum, theemulsions within said set having substantially the same speed; a secondset of silver halide photosensitive emulsions coated in layers abovesaid first set, the emulsions in the second set having substantially thesame spectral response as the emulsions of the first set; and a neutraldensity filter disposed intermediate the two sets, the attenuatingeffect of said filter being to shift the speed of the emulsions of thelower set a predetermined amount to provide the sets of emulsions withcomplementary speeds.
 9. A color photographic film as claimed in claim 8in which said first and second sets of emulsions have substantially thesame photographic speed.
 10. A color photographic film as claimed inclaim 8 in which the second set of emulsions are fast ammoniacalemulsions.
 11. A color photographic film comprising: a film support; twosets of silver halide photosensitive emulsions coated in layers uponsaid film support, each set containing a red-sensitive emulsion, agreen-sensitive emulsion and a blue-sensitive emulsion; and a neutraldensity filter disposed between the two sets of emulsions, theattenuating effect of the filter being, to shift the speed of the lowerset of emulsions a predetermined amount To provide the two sets ofemulsions with complementary speeds.